GADD153 is a highly conserved mammalian gene whose expression is increased in response to a variety of stresses including growth arrest and DNA damage. It is a member of the CCAAT/enhancer-binding protein (C/EBP) family of transcriptional activators and can dimerize with other C/EBPs through a leucine zipper domain. However, in contrast to other C/EBPs, it lacks the ability to bind to CCAAT DNA sequences and has therefore been proposed to serve as a negative regulator of other members of this family (by virtue of its ability to heterodimerize with them and inhibit their binding to DNA). Studies in this project have focused on the regulation and function of GADD153 expression in response to stress. The approaches taken have included (1) characterization of Gadd153 expression (and that of other C/EBPs) in response to diverse growth inhibitory and metabolic stimuli including PGA/2-mediated growth arrest, glucose deprivation, DNA damage, and inducers of the acute phase response in vivo and in vitro; (2) use of yeast hybrid protein systems to examine the interaction between the GADD153 protein and other members of the C/EBP family, and (3) development of transgenic models to address the expression and role of GADD153 during development and in response to stress in vivo. Of particular interest is our finding that the GADD153 protein provides a functional transactivation domain when fused to a yeast GAL4 transcription factor DNA binding site, suggesting that GADD153 can act directly (rather than as a dominant negative inhibitor as suggested above) to influence transcription perhaps through as yet unidentified sites. Using the yeast two hybrid system, we have found that in contrast to other C/EBP family members, GADD153 appears to be unable to form homodimers, suggesting that it must interact with other transcription factors to influence gene expression, or be functional as a monomer.